Surface treating apparatus



y 1952 L. H. BISHOP ET AL SURFACE TREATING APPARATUS 5 Sheets-Sheet 1Filed Dec. 27, 1948 DusT COLLECTOR INVENTORS BISHOP Fl/V/V ATTOR/Vf) y1952 L. H. BISHOP ET AL 2,597,434

SURFACE TREATING APPARATUS Filed Dec. 2'7, 1948 5 Sheets-Sheet 2 25 i T'2 0 Z INVENTOR LEW/5 H. BISHOP 5 JOHN S. FINN A TTOR/VEY y 0, 1952 H.BISHOP ET AL 2,597,434

' SURFACE TREATING APPARATUS Filed Dec. 27, 1948 a Sheets-Sheet 5 a/IIOM IN ENTO LEW/5 H. B/ HOP JOHN S. FIN/V ATTORNEY Patented May 20,1952 SURFACE TREATING APPARATUS Lewis H. Bishop and John S. Finn,Burlingame, Calif., assignors, by mesne assignments, to William H. Mead,Oakland, Calif.

Application December 2'7, 1348, Serial No. 67,462

11 Claims. (Cl. 51-12) This invention relates to a method for continfacetreating methods and apparatus of the type I described in the patent toWilliam H. Mead, No. 2,455,514, issued December 7, 1948. That devicesimultaneously impels treating material against a surface andsuction-removes the spent abrasive and waste material. By employing agrit reclaimer, such as that described in the copending application No.778,378, filed October 7, 1947, the spent abrasive can be separated fromthe-waste material and re-used.

The problems solved by this present invention are those having to dowith makin possible continuous operation of such or similar apparatus,The problems arise from the fact that the abrasive, which is impelledagainst a surface by a high-pressure blast of air or by an impellerwheel and is removed from-the surface bya vacuum pump, carries alongwith it the waste inaterial which is abraded from the surface. Theabrasive grit is next separated from the waste material while stillunder extremely low pressure conditions. One problem'which had to besolved before the apparatus could operate continuously was how torestore the" abrasive from the low pressure atmospherewithout eitherinterfering with the low pressure conditions'in the abrasive-removingline, or reducing the high pressure in the abrasive-impelling line.

Heretofore, it was necessary to shut ofi the machine during suchtransfer, so that the pressure in the blast line dropped to atmospheric2 the operator had to stop the machine to refill the hopper.-

One important object of this invention is to provide an apparatusenabling continuous operation of such a machine. This inventionautomatically replenishes the feed hopper during use, and there is noneed to interrupt operations for refilling the hopper.

Another object of the invention is to provide an apparatus fortransferring material between chambers under different pressureconditions.

Another object of the invention is to provide a transfer apparatus ofthe type described which will not adversely affect the pressureconditions in the chambers.

Another object of the apparatus is to provide an apparatus fortransferring granular material from a low pressure chamber to ahigh-pressure chamber without substantially altering the pressureconditions in either chamber.

" A further object of the invention is to provide an automatic transferdevice of the type described.

Another object of the invention is to provide a time-controlled transferapparatus.

A further object of the invention is to provide an apparatus suitablefor continuous sand-blasting with a relatively small quantity of grit.

A further .object is to achieve continuous sand blasting over a longperiod of time, without having to supplement a relatively small, mobilesupply of abrasive. I

' Other objects and advantages of the invention will appear from thefollowing detailed description of an embodiment, presented in accordancewith U. S. Revised Statutes, Sec. 4888. It is appreciated that changesin detail may be made in accordance with the principles set forth, sothat a machine differing in some details-from this embodiment wouldstill be within the spirit of the invention as described in the appendedclaims.

In the drawings:

Fig. 1 is a view in elevation, partly in section, of a continuoussurface treating apparatus embodying the principles of the invention;

Fig. 2 is a diagram of the piping circuit in the transfer apparatus;

Fig. 3 is a diagram of the electrical circuit employed;

Fig. 4 is an enlarged view in elevation and in section of the lower dumpvalve; and

Fig. 5 is a view in perspective and in section of the apparatus in thevicinity of the lower dump valve.

The apparatus employs an intermediate chamber between the low pressurereclaimer hopper and the high pressure feed hopper. By connecting theintermediate chamber to only one of the said chambers at a time, thematerial is transferred first from the low pressure hopper to theintermediate chamber and subsequently from'th'e intermediate chamber tothe feed hopper. The pressure of the intermediate chamber is raisedbefore the valve to the high pressure chamber is to be open, and afterthis valve is; closed the pressure in the chamber is reduced before thevalve to the low pressure chamber isopened. All of these valves andpressure adaptors are controlled by a timing device which alternatesthem according to a predetermined cycle. 7 I

Fig. 1 shows a device embodying the principles of this invention used inconjunction with'a'surface-treating apparatus .of the type describedmore fully in'Patent No.:2,'455;514. A compressor sends air underpressure through aeonduit At a manifold |2 the air eurrentis'divided, aconduit |3 shunting some of the air into a grit feed hopper l4, whilethe rest of the airifed through a conduit |5 into a grit-feed valve Hi.This valve I6 is preferably of a type described in the copendingapplication by William H. Mead, Sei', No. 55,243, filed October 18,1948,-which'issued as Patent No. 2,521,931, dated September 12, 1950.Grit is introduced from the hopper into the blast current at the valvel5 and is fed through a conduit I! to an operating head l8, where it isimpelled against .asurfacel 9.

A suction pump draws the spent abrasive and waste material (such aspaint flakes, rust, sawdust, etc.) out of the head l8 through a suctionconduit 2| into a grit reclaimer 22, preferablyoi the type disclosed inpending application Serial No. 778,378, filed October 7, 1947. Here theabrasive and waste are separated, and the waste is carried out through aconduit 23 to any form of dust collector. The reclaimed abrasive fallsdown into a reclaimer hopper 25, still under'nearvacuum conditions.

Between the reclaimer hopper 25 and the feed hopper I4 is positioned anintermediat transfer chamber 30. At its upper end is an upper dump valve3|, and at its lower end is a lower dump valve 32. Both valves 3| and 32comprise airactuated, cone-shaped plugs 33, which are closed against therespective openings 34 or 35by' compressed air entering through openings33 at the lower end of the valves.

The upper valve 3| opens by a combination of spring pressure andgravity, dropping when the air pressure inside the valve falls below acertain level, and then permits grit to fall from the reclaimer hopper25 into the intermediate transfer chamber 30.

The lower valve 32 is adapted for quicker and more positive control. Asshown in Fig. 4, the lower valve 32 is supported by a housing 31 whichis suspended from the feed hopper housing H. The lower end of thehousing 31 is closed except for the-opening '35, and the upper end isalso closed, preferably by a hood 38. A valve stem 40, which dependsfrom the "cone 33, is slidable up and down through an opening 4| in thehood 38. To prevent grit from working down through the opening 4|, aflexible, collapsible sleeve or boot 42 is secured tightly around thestem 48 and around the opening 4|.

Below the hood 38 is an annular flexible-din phr-agm 43. Its innerperiphery is secured to the stem and its outer periphery is secured tothe 4 housing 31. The diaphragm 43 and the hood 38 enclose an upperchamber 44, having an opening 45 through which compressed air may enterfrom the duct 31, in a manner to be explained. Below the diaphragm is alower chamber 46, open only to the air pressure inlet 36.

A stretched spring 41 surrounds the stem 43 inthe lower chamber 46. Thelower end 52 of the spring 41 is secured to the stem 40, while upper end53 of the spring is anchored to the valve housing 37. The spring 41biases the valve 32 downwarciytcward its open position. The force ofthe-spring 41 augments the force of gravity an'd aids in providing aquicker opening action a'galnst'the'Trictionof the stem 40 in its guides-4| and. and the force necessary to compress the boot.

Preferably the spring 41 is a light one; for example, a very successfulvalve uses a spring which exerts "a force of about ten .pounds. When theblastilineis operated at p. s. i., a typical diaphragm 43 (having anarea of 20 square inches) will be iorced up with 2000 lbs. pressure byair inthechamber-46. Thus the spring will not open the valve until theair pressure in the upper chamber-reaches about 1990 lbs., or 99.5 p. s.'i. Due to this relationship, the valve 32 and the whole apparatusmay beoperated over a very wide range of pressures without changing the spring41, and the valve 32 will not open until the pressureinchamber 44almostbalances the pressure inchamber 46.

The chamber 46 is kept under pressure continuously during operation ofthe machine, and this air pressure holds the cone 33 normally up againstthe'opening '35. However, when the air pressure in the upper chamber 44(in a manner to be described) balances the air pressure in the lowerchamber 46, the weight of the cone and other moving. parts overbalancesthe spring 41 and the cone 33 drops, opening the valve 32.

A baiile [plate 48, 49 is positioned above each opening 34, 35 justabove where the point of the cone 33 rests when the cone is in its upperor closed position. These'baffles 48, 49 prevent the grit from stackingup over the openings 34, 35 and keep the space above the openings freeso that the cones 33 'canclose quickly and easily. Otherwise, when thepressure changes in the chamber 30 there might-be disruption of thesystem hy'a leak from the high pressure chamber 14 .into the lowerpressure chamber 25. Allthe grit must pass through the spaces 50 betweenthe periphery of the baffle plates and the hopper walls: f Then itslides down the inclined hopper walls andfinto the verticalopening.

Preferably a shroud 5| hangs down underneath-and-around-each opening 34and 35 to keep grit out of the air openings adjacent the upper ends ofthe hoppers l4 and 30.

The pressure in the reclaimer hopper 25 is normally about ten inches ofmercury, while the pressure in the feed hopper chamber |4, duringtypical operating conditions, is normally kept at about'one hundredpounds per square inch; therefore, valves 31 and 32 are never allowed toopen at'the same time while the apparatus is operating. Moreover, theair inside theintermediate chamber 30 is brought to a pressureapproaching the pressure in the feed hopper |4 (approximately onehundred pounds per square inch in this case) before. the valve 32-isopened.- The pressure-is reduced after thevalve closes and before thevalve-opens. These conditions are obtained by means of the pressurecontrol circuits shown in Fig. 2 andthe electrical control circuitsshown 6| on the operating head I8. This switch 6| is thus used to shutthe blast line off and on; it

may also, if desired, be used to turn on and ofi the timing mechanism80.

Between the valve 60 and the T fitting I2 on the conduit I I is an Xfitting 62. At the fitting 62 two conduits 63 and 64 open off the lineII The conduit 63 leads to the lower opening 36 of the lower dump valve32 and air pressure therein urges the valve 32 toward a closed positionwhen the machine is operating.

The conduit 64 leads through a second solenoid valve 65, which canefiect control of the valves 3| and 32 as well as the pressure insidethe intermediate chamber 30. Beyond the solenoid valve 65, is another Xfitting 66, from which three conduits 61, 68 and 69 lead out. Theconduit 6'! leads to the opening 45 in the upper chamber 44 of the lowerdump valve 32. Compressed air which passes through the solenoid valve 65is conducted to the chamber 44 and opens the valve 32. The pressuresabove and below the diaphragm 43 balance each other and gravity and thespring 41 open the valve 32. r

The conduit 68 leads to a third solenoid valve I0, and thence vents tothe atmosphere when the valve I6 is open. The solenoid valve I0 isopened only when and at the same moment as the solenoid valve 65 isclosed, and at that time quickly bleeds the air from the chamber 44, sothat the lower valve 32 closes.

The conduit 69 leads up through a check valve II (which prevents airfrom flowing backwards through the conduit 69 and out the valve I0 whenthe latter is open) to a T fitting I2. There, the conduit 69 is dividedinto a conduit I3 passing into the tank 30 and a conduit I4 leading tothe dump valve 3|. Thus, when the solenoid valve 65 is open, the valve3| is closed almost immediately and when the pressure inside the tank 30reaches approximately the level of the pressure inside the hopper I4,the valve 32 opens.

Preferably the conduits are of sufliciently small diameter so that thepressure does not build up instantaneously in the upper chamber 46 ofthe valve 32 or inside the intermediate chamber 36. After the valve 3|has closed, three or four seconds may elapse before the pressure in thechamber 46 and in the chamber 30 approximates the pressure in the hopperI4. In this way there will be no drop in pressure when the valve 32opens. Otherwise, there will not be complete continuity, and a portionof the surface I9 may be skipped and not treated during the timenecessary to equalize the pressure. This is one problem which thepresent device solves in the manner just indicated.

A bleed conduit 15 leads out from the tank 30 through a strainer I6 to asolenoid valve 11, and when the valve 11 is open, air may pass outthrough a muiiier I8 to the open air. The strainer I6 prevents any gritfrom getting into solenoid I1 and damaging it, and the check valve IIperforms the same function for the solenoid valve I6. The muffler I8silences the noise from the rush of air.

Since the solenoid valve 60 is open whenever the machine is operatingtheair current then flows through the blast conduit I1 and through theconduit 63 to fill the lower chamber 46 of the dump valve 32 to hold itclosed. The other 6 three solenoid valves 65, III and 11 are controlledby a timer 80. When the valve 65 is open, the valves I6 and 11 areclosed, and vice versa.

The electrical circuit is shown in Fig. 3. Preferably a three line A. C.supply is used, with one wire 8| grounded. From the second side 82 andthe third side 83 of a 110-volt A. C. supply, wires 84 and 85 lead to a110-volt-6-volt transformer 86. From each pole of the 6-volt side, wires81 and 86 lead to a 6-volt relay 89, line 88 passing through the masterswitch 6|. From one pole of the relay actuator, a wire 96 leads to theside 82 of the 110 volt input line. From the other side of the relayactuator 89, one wire 9| leads to the master solenoid 66, and anotherwire 92 leads to post 93 of the timer 80. The solenoid 60 is thusindependent from the timer 80, but both the timer 80 and the valve 66are energized by the switch 6|. When the current is on, the valve 66 isalways open, and the timer 80 operates continuously.

Wires 94, 95 and 96 each lead from the timer post 93 to one side of thesolenoids 65, I0 and 11, respectively. Wires 91 and 98 lead back fromthe opposite sides of the solenoids I0 and TI to a switch element 99 ofthe timer 86, and a wire I66 leads from the opposite side ofthe-solenoid 65 to a switch element |6| on the timer 80. Another wire|02 leads from the timer post I63 to the A. C. line 82.

All three solenoids 65, I0 and I1 operate simultaneously but not in thesame direction. That is, when the circuit controlling the valve 65 isclosed so that the valve 65 is open, the circuit controlling the valvesI0 and I1 is open so that the valves I0 and 11 are closed. Air will thenpass into and be confined in the tank 30. When the circuit controllingthe valve 65 is open, the valve 65 is closed, and no air passes beyondit. Simultaneously, the other circuit is closed, and the valve I6 isopened to bleed oil" the valve 32 so that the latter closes almostinstantly on a short drop in pressure. ously opens the valve 11 to bleedout the tank 30 and valve 3|, which opens when the pressure has dropped.

In operation, when the master switch 6| is turned on, the solenoid valve60 is opened to admit air from the compressor I6 through the conduit IIto the feed tank I4 and feed valve I6, so that abrasive is sent to thehead I8. At the same time, the timer 86 is started and runs its cycle.

For convenience, we shall assume that the solenoid valve 65 is closed tobegin with. Therefore, no air flowsfrom the conduit II into the conduit64, and consequently none flows in the conduits 61, I3 and I4. The upperdump valve 3| is held open by its spring and by gravity. The lower dumpvalve 32 is closed, because there is no pressure in the upper chamber 44and the lower chamber 46 isunder high pressure. The suction pump 20 isoperating, and it keeps the reclaimer hopper 25 at a vacuum of about 10inches of mercury. Any reclaimed grit remaining in the reclaimer 25falls through the slits 50 around the edges of the plate 48 and isstored in the tank 30.

After a period of time determined to occur before all thegrit is usedout of the tank I4 the timer 80 throws a switch which opens the solenoid65 and closes the solenoids I6 and I1. Air then flowsfrom the conduit I,through the con 'duit 64, mm the conduits 61, I3 and I4. From theconduit 74 air passes into-the upper dump The same circuitsimultanevalve 31. and closes it almost immediately. Air Passing throughthe conduit 13 fills the tank 30, and the pressure soon approaches andequals the pressure in the feed hopper 14. At the same time, air fillsthe upper chamber 44 of the valve 32, and when it reaches a pressureclosely approaching that in chamber 46, the valve is opened by itsspring 41 and its co-acting forces. Grit inside the tank 30 can thenfall down through the slits 50 around the baflle 49 and down into thefeed hopper, l4, replenishing it without interfering with the pressureconditions in the blast line. y, 4

When the timerSO reaches another predetermined position, the solenoidvalve 65 is closed and the valves 10 and H are opened. Conduits 61, 13and 14 are cut off from their supply of air, while'conduits 68 and 15are opened to the atmosphere. Airimmediately bleeds out of the upperchamber 44 of the lower dump valve 32, while the check valve H preventsany cushioning efiect from the conduits 73 and 14. When the pressure hasdropped only a short way (usually a pound, or less) the air pressure inthe chamber 46 closes the lower dump valve 32. The air in the tank 30fiows to atmosphere out the conduit l through the strainer 16, solenoidvalve 11, and muffler l8. Simultaneously the air in the upper dump valve3| fiows back through the conduit 14 into the conduit 13, through thetank 30 and the conduit 15, and out to atmosphere. When the pressure islow enough (i. e., approaching atmospheric), the upper dump valve 3!opens, and what little air remains is immediately sucked out by the pump20. In a typical installation the pump 20 draws 300 cubic feet of airper minute. Since the volume of the chamber 30 is only a cubic foot orso, this small pressure differential. will not affect the operation atthe head. When the valve 3| opens, the grit stored up in the chamber25may then fall down again into the chamber 30, completing the cycle.

What is claimed is:

1. An apparatus for continuous abrasive-blasting, comprising a feedhopper for storing abrasive material, an air blast line, a feed valvefor feeding said material into said line, an operating head where saidmaterial is impinged against a surface, a suction line for withdrawingsaid material and waste from said surface, a separator for salvagingsaid material out of said waste, a reclaimer hopper for receiving saidwithdrawn material, an intermediate hopper between said reclaimer hopperand said feed hopper, a first transfer valve between said reclaimerhopper and said intermediate hopper, a second transfer valve betweensaid intermediate hopper and said feed hopper, a timing device, and anelectrical relay operated by said timing device to alternately closesaid first valve and open said second valve and close said second valveand open said first valve.

2. An apparatus for continuous abrasive-blasting, comprising a feedhopper for storing abrasive material, an air blast line, a feed valvefor feeding said material into said line, an operating head where saidmaterial is impinged against a surface, a suction line for withdrawingsaid material and waste from said surface, a separator for salvagingsaid material out of said waste, a reclaimer hopper for receiving saidsalvaged material, an intermediate hopper between said reclaimer hopperand said feed hopper, a first transfer valve between said reclaimerhopper and said intermediatehopper, a second transfer valve between saidintermediate hopper and said feed hopper, a timing device, an electricalrelay operated by said timing device to alternately close said firstvalve and open said second valve and close said second valve and opensaid first valve, means to admit air to said intermediate hopper whensaid first valve is closed, and means to bleed air from saidintermediate hopper when said second valve is closed.

3. An apparatus for transferring granular material from a low pressurechamber to a high pressure chamber, comprising an intermediate chamberplaced below said low pressure chamber and above said high pressurechamber, a first valve between said intermediate chamber and said lowpressure chamber,-a second valve between said intermediate chamber andsaid high pressure chamber, a timing device, and means operated by saidtiming device for alternately opening said first valve while said secondvalve is closed and opening said second valve while said first valve isclosed.

4. The apparatus of claim 3 in which there is mean controlled by saidtimer for increasing the pressure in said intermediate chamber betweenthe time said first valve closes and the time said second valve opens,and means controlled by said timer for reducing the pressure in saidintermediate chamber between the time said second valve closes and thetime said first valve opens.

5. An apparatus for transferring granular material from a low pressurechamber to a high pressure chamber, comprising an intermediate chamberplaced below said low pressure chamber and above said high pressurechamber, a first valve between said intermediate chamber and said lowpressure chamber, a second valve between said intermediate chamber andsaid high pressure chamber, a timing device, and an electrical relaycontrol operated by said timing device for alternately opening saidfirst valve while said second valve is closed and opening said secondvalve while said first valve is closed.

6. An apparatus for transferring granular material from a low pressurechamber to a chamber maintained at high pressure by a high pressure linewithout upsetting the pressures concerned, comprising an intermediatechamber placed below said low pressure chamber and above said highpressure chamber; an air operated valve between said intermediatechamber and each of the other said chambers; a first solenoid valveadapted to open for simultaneously admitting air from said high pressureline to the upper of said valves to close it and for admitting air fromsaid high pressure line to said intermediate chamber to build up thepressure therein and for admitting air from said high pressure line tosaid lower valve to open it when its pressure and the pressure in saidintermediate chamber reach a predetermined value, said solenoid valvealso being adapted to close for simultaneously cutting off all air fromthe high pressure line to said valves and said intermediate chamber; asecond solenoid valve adapted to open to bleed air from said lower valveto close it; a third solenoid valve adapted to open for bleeding airfrom said intermediate chamber so that its pressure may be reduced andfrom said upper valve so that it may open when its pressure drops belowa certain point; an electrical circuit to operate said solenoid valves;and a timer which adapted to alternately open said first solenoid valveand simultaneously close said second and third solenoid valves for onepart of a cycle, and to close said first solenoid valve andsimultaneously open said second and third solenoid valves over anotherpart of said cycle.

7. An apparatus for continuous abrasive-blasting, comprising: a feedhopper for storing abrasive material; an air blast conduit; means forfeeding said material into said conduit; means for impinging saidmaterial from said conduit against a surface to be treated; means forwithdrawing said material from said surface; a reclaimer hopper forreceiving said withdrawn material; an intermediate hopper between saidreclaimer hopper and said feed hopper; a first transfer valve betweensaid reclaimer hopper and said intermediate hopper; a second transfervalve between said intermediate hopper and said feed hopper; a timingdevice; and means actuated by said timing device for alternately closingsaid first valve and opening said second valve, and closing said secondvalve and opening said first valve.

8. An apparatus for continuous abrasiveblasting, comprising a feedhopper for storing abrasive material; an air blast conduit; means forfeeding said material into said conduit; means for impinging saidmaterial from said conduit against a surface; means for withdrawing saidmaterial from said surface; a reclaimer hopper for receiving saidwithdrawn material; an intermediate hopper between said reclaimer hopperand said feed hopper; a first transfer valve between said reclaimerhopper and said intermedi ate hopper; a second transfer valve betweensaid intermediate hopper and said feed hopper; a timing device; meansactuated by said timing device for alternately closing said first valveand opening said second valve, and closing said second valve and openingsaid first valve; means for admitting air to said intermediate hopperwhen said first valve is closed; and means for bleeding air from saidintermediate hopper when said second valve is closed.

9. An apparatus for transferring granular material from a first chamberto a second chamber, comprising an intermediate chamber placed betweensaid first and second chambers; a first valve between said intermediatechamber and said first chamber; a second valve between said intermediatechamber and said second chamber; a timing device; and means operated bysaid timing device for alternately opening said first valve while saidsecond valve is closed and opening said second valve while said firstvalve is closed.

10. The apparatus of claim 9 in which there is means controlled by saidtimer for increasing the pressure in said intermediate chamber betweenthe time said first valve closes and the time mediate: chamber betweenthe time said second valve closes and the time said first valve opens.

11. An apparatus for transferring granular material from a low pressurechamber to a chamber maintained at high pressure by a high pressureline, without upsetting the pressures concerned, comprising anintermediate chamber placed below said low pressure chamber and abovesaid high pressure chamber; a pair of pneumatic valves, one beinglocated between said intermediate chamber and each of the othersaidchambers to open and close the passages between said chambers; afirst control valve adapted when opened to simultaneously admit gas fromsaid high pressure line to the upper of said pneumatic valves to closeit and to admit gas from said high pressure line to said intermediatechamber to build up the pressure therein and to admit gas from said highpressure line to the lower of said pneumatic valves to open it when itspressure and the pressure in said intermediate chamber reach apredetermined value, said first control valve also being adapted whenclosed to simultaneously cut off all gas from the high pressure line tosaid pneumatic valves and said intermediate chamber; a second controlvalve adapted when opened to bleed gas from said lower pneumatic valveto close it; a third control valve adapted when opened to bleed gas fromsaid intermediate chamber so that its pressure may be reduced and fromsaid upper pneumatic valve so that it may open when its pressure dropsbelow a certain amount; and timing means adapted to alternately opensaid first control valve and simultaneously close said second and thirdcontrol valves for one part of a cycle, and to close said first controlvalve and simultaneously open said second and third control valves foranother part of said cycle.

LEWIS H. BISHOP. JOHN S. FINN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Niunber Name Date 584,021 Tilghman June 8, 1897681,867 Bardwell Sept. 3, 1901 1,706,737 Moore Mar. 26, 1929 1,752,664Forcier Apr. 1, 1930 1,814,616 Boesger July 14, 1931 FOREIGN PATENTSNumber Country Date 459,086 France Aug. 25, 1913

